Amazon.com Inc. on Thursday delivered the largest quarterly profit in its 20-year history, but investors apparently are thirsty for more after subsisting on thin margins for years.

The online retailer’s shares plunged as much as 15% in after-hours trading, erasing more than $30 billion in market value despite a profit that more than doubled to $482 million in the holiday period. It was also the third straight quarter of profits, the first time Amazon has done so in more than three years.

The failure to meet outsize expectations underscores the pressure Amazon now faces after teasing Wall Street in recent quarters with tighter costs and black ink. Amazon until recently put nearly every dollar it generated back into the business.

The company was one of the big growth stories among technology stocks in 2015, more than doubling its market value to over $300 billion last year and easily outperforming other tech giants like Alphabet Inc., Apple Inc. and Facebook Inc.

. . . .

For the year, Amazon passed $100 billion in revenue for the first time in its two-decade history. It took rival Wal-Mart Stores Inc. 35 years to reach the same mark in 1997, two years after Amazon.com opened for business.

Amazon has captured more customers by aggressively building out new warehouses near urban centers to speed deliveries and by bulking up its Prime unlimited shipping membership with streaming video and other benefits.

And it has built up a huge lead on rivals in offering cloud-computing services through its lucrative Amazon Web Services unit, which rents computing power to other companies from thousands of servers. Sales from that business jumped 69% to $2.4 billion, while operating profit nearly tripled to $687 million, reinforcing its place as Amazon’s fast-rising growth engine. Still, AWS’s revenue growth slowed from 78% in the previous three months as Amazon drained more costs.

. . . .

The company said nearly half of the units of merchandise it sold in the quarter came from third-party sellers who store their goods in Amazon warehouses. That is good news for Amazon because most observers assume such sales are generally more profitable than the merchandise it purchases itself for resale.

Guess those folks bailing out are short-termers. I’m in for the long haul. Last I looked today (12:30-ish Eastern time), the stock was down 52, the same amount it went up yesterday. I was watching after the bell trading until last night. The biggest drop I saw was -85.

Partly, but moreso it’s “Amazon disappoints analysts.” Because that’s who had “outsize expectations” in the first place.

There are a lot of people getting paid a lot of money to be completely wrong about markets and value right now. If you follow tech blogs, you see it all the time. Amazon wasn’t the only one who “disappointed”; analysts were also disappointed by Apple’s earnings reported on a record-breaking quarter of revenue.

See also every headline that “reports” Apple delayed some as-yet-unannounced iDevice or other.

So yes, in the end the shareholders were disappointed, but only because those analysts were disappointed, because they don’t know much about (as Matt notes) how to determine the value of a company. Because one would think that, technically, given Amazon doubled its profit, those stocks would be worth more. That they weren’t is solely because those analysts’ incorrect guesses disappointed other people who were considering buying the stocks.

The analysts do know how to value a company. It’s the novices like most of us that don’t. Also it’s the institutional investors that are controlling the market price of the stock; not the small time investors. How many shares of Amazon stock could an average person afford to buy?

Lots of people buy stock based on an expected set of future events. Their evaluation is based on those events happening. When they don’t, they acknowledge their expectations were wrong, and adjust their evaluation to what actually happened.

Buyers bid on what actually happened. The stock price falls. This is normal price-discovery stuff that happens everyday in auction markets.

This is common with many tech companies. Apple set record profits as well but the stock went down based on future expectations. Amazon dropped almost 8% today but Microsoft was up 6% on better than expected performance and Facebook was up as well because of enormous profits.